=Paper= {{Paper |id=Vol-1815/paper9 |storemode=property |title=Reducing Noise Sensitivity of Formal Analogical Reasoning Applied to Language Transfers |pdfUrl=https://ceur-ws.org/Vol-1815/paper9.pdf |volume=Vol-1815 |authors=Vincent Letard,Gabriel Illouz,Sophie Rosset |dblpUrl=https://dblp.org/rec/conf/iccbr/LetardIR16 }} ==Reducing Noise Sensitivity of Formal Analogical Reasoning Applied to Language Transfers== https://ceur-ws.org/Vol-1815/paper9.pdf
                                                                                                       87




Reducing Noise Sensitivity of Formal Analogical
   Reasoning Applied to Language Transfer

               Vincent Letard1,2 , Gabriel Illouz1,2 , and Sophie Rosset1
                           1
                               LIMSI, CNRS, Université Paris Saclay
                                 firstname.lastname@limsi.fr
                 2
                     Université de Paris-Sud, F-91405 Orsay Cedex, France



        Abstract. Previous applications of formal analogical reasoning to the
        task of natural to formal language transfer have shown a very high pre-
        cision. However, this also came with a low recall. Analogical reasoning
        methods are very sensitive to noise in the input data. In order to im-
        prove the response rate, we propose to release the constraints. Firstly,
        we present a relaxation of the search in the example base. Secondly,
        we adapt a dynamic programming resolution algorithm from an exist-
        ing work. We then discuss the genericity obtained. The results show the
        expected increase in recall. In particular, the first relaxation shows an
        interesting improvement of the correct answers.


1    Introduction

The design of interactive assistants is a nowadays trend as more and more com-
plex procedures are operated using computers. In this work, we consider the
applicative goal is of giving instructions to the computer in natural language, as
shown in the example below for English and bash.
                     “Print 14 copies of ex08.pdf ” ! lp -n 14 ex08.pdf

This task is meant for an interactive application, where the user needs to perform
operations but does not know or cannot remember the right command.
    This paper focuses on transferring user specific language, or idiolects, into
formal language. The experimental context is seen as a task of machine transla-
tion: natural to formal language transfer.
    Example-based machine translation (EBMT) is a good candidate to address
this task, as it adapts well to new, specific domains with few examples. Among
them, formal analogical reasoning (FAR) operates directly on mere surface forms.
The precision obtained is also quite high [8]. Analogy is known to be a crucial
mechanism to human cognition [3]. However, the framework of FAR has lim-
itations. Firstly, the complexity of the exhaustive computation is high. Some
heuristics and optimization have been proposed. Secondly, the constraints on the
input examples are strong. This makes formal analogy very sensitive to noise.
The system remains silent when the input does not perfectly form an analogy
with the examples from the base.



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                                                                                      88




   We propose two approximations to reduce noise sensitivity. The first one
helps to consider more examples from the base even if they do not form an
analogy per se. The second one allows approximating the process of resolution.
Our hypothesis is that relaxing the strong constraints on FAR increases the
recall and hopefully gives new, meaningful answers.
   In the next section, we give some general context related to EBMT and
FAR. The latter is introduced in more details in section 3. Our contributions are
detailed in sections 4 and 5, after introducing their contexts. Section 6 describes
the associated experiments. Finally, section 7 is dedicated to interpreting the
results in comparison with related work.


2     Background
Example-based approaches to machine translation received an increasing interest
since Nagao’s paper [12]. EBMT and translation by analogy have been used as
synonyms until the definition of formal models for analogical proportions [7, 14,
15]. This model is associated with a framework of two main algorithms, one for
the resolution and the other for the validation of analogies. They are used to
build the answer using a triplet of sentences. The task of natural (NL) to formal
language (FL) transfer has already been tackled in [5], and [1, 2, 4] consider the
mapping of instructions directly to an action model.
    FAR algorithms are computationally demanding. E↵orts have been made in
the direction of reducing the computation time for the phase of searching in
the example base. In order to prevent slowing down on big example bases, sev-
eral heuristics have been used to guide and prune the search [8, 9]. A review
of the heuristics for FAR is given in [13]. Langlais and Yvon [6] proposed an
optimization based on the structure of count tree. It relies on the preservation
of analogical proportions through morphism. We based our work on this opti-
mization, more details are given in section 4.
    Regarding the issue noise sensitivity, [11] proposed a general algorithm for
solving formal analogical equations with the best approximation, according to a
notion of analogical dissimilarity. It is presented in section 5.1.
    [10] already applied FAR to the task of natural to formal language transfer.
This work is used here as a baseline to assess our experimental results.


3     Formal Analogy for Language Transfer
3.1   Analogical Proportions on Sequences
A proportional analogy is a relation between 4 elements that can be stated in
natural language as the expression “X is to Y as Z is to T”. As an illustration,
the following quadruplet is an analogical proportion over the domain of word
sequences: “Display f.txt is to cat f.txt as Display file is to cat file”. We
use the notation [X : Y :: Z : T ], for a valid proportion, and [X : Y :: Z : ?]
for an analogical equation. These objects are processed using the operations of
                                                                                       89




verification of a proportion, and resolution of an equation. When applied
to sequences, these operations rely on the identification of an alignment of the
symbols. Each atomic alignment of symbols must be of one of the following
alternating forms1 : (a, b, a, b) or (a, a, b, b). A proportion is verified (valid)
if it can be obtained from a concatenation of proportional atomic alignments.
A sequence is a solution of an equation if the resulting proportion is verified.
The solution to an analogical equation is often not unique, therefore the solution
is selected from the shortest alignment as it is considered [14, 13] to produce a
satisfying answer.
     The exponential number of n to n alignments between sequences makes the
naive algorithms not usable in real conditions. Efficient algorithms for perform-
ing the operations of validation and resolution are described in [14, 15]. Their
complexity is in O(n3 ), n being the size of the longest sequence.
     Typically, the solving algorithms work by filling a three dimensional matrix
of size |X| ⇥ |Y | ⇥ |Z| where [X : Y :: Z : ?] is the equation to be solved.
The search in the matrix corresponds to the concurrent and ordered iteration
over the symbols of the three sequences with the following legal transitions:
  – reading identical symbols on X and Y
  – reading identical symbols on X and Z
  – reading a symbol on Y and outputting it
  – reading a symbol on Z and outputting it
     Note that the symbols can be characters, words, or any kind of predefined
segment. The details of the algorithms are given using the term “symbol” to
emphasize on their genericity.


3.2    Language Transfer

FAR can be applied to the problem of language transfer by processing sentences
as sequences of symbols. In our case, the sentences are NL requests and FL
commands, and the symbols are words. Here, we call command (ci ) the string
of characters that is typed by the user in the terminal (e.g. “ls -l folder/”).
Similarly, we call request (ri ) the whole string of characters that is submitted by
the user. The example base B is a set of paired sentences. The request domain R
is French2 and the command domain C is bash. B ⇢ (R ⇥ C) Given a request
r 2 R, the base is searched for analogies in order to generate an answer s. We
can search directly for equations [ri : ci :: r : ?] or indirectly, for proportions
[ri : rj :: rk : r] in order to solve the associated equation [ci : cj :: ck : ?].
     These strategies are illustrated in examples 1.1 and 1.2. They are referred
to as the direct and the indirect strategies respectively. The first example
gives the solution “lp -n 2 file.pdf”, obtained by mixing languages, while
the second one produces “gcc f.c” only using the bash part of known forms.
Both strategies allow the production of relevant, unseen commands, and are also
complementary [10].
1
    a or b can be the empty symbol ✏.
2
    The examples are given in English for convenience.
                                                                                          90




                 (ri ) Print 14 copies of ex08.pdf : (ci ) lp -n 14 ex08.pdf
                                                   ::
                 (r) Print 2 copies of file.pdf     :            ?

                    Example 1.1: Direct analogical resolution

              (ri ) Count the lines in f.c : (rj ) Count the lines in the C file f
                                           ::
              (rk ) Compile f.c            :       (r) Compile the C file f


              (ci ) wc -l f.c              :            (cj ) wc -l f.c
                                          ::
              (ck ) gcc f.c                :                   ?
                   Example 1.2: Indirect analogical resolution

    In the next two sections we present approaches for optimizing search and
relaxing the analogical resolution.


4     Exploring the Example Base

This section describes the tree-count search algorithm, proposed by Langlais and
Yvon [6], and our adaptation for relaxing its associated constraints.


4.1   Tree-Count Search

The algorithm relies on the following property of formal analogy:

                      [X : Y :: Z : T ] ) |X| + |T | = |Y | + |Z|

That is, the count of symbols in X and T equals that in Y and Z. This also
stands for any specific symbol of the lexicon L (L is the set of all the symbols
appearing in B).

               [X : Y :: Z : T ] ) 8s 2 L |X|s + |T |s = |Y |s + |Z|s

    The tree-count is built by assigning each form to be indexed to the path in
the tree corresponding to the count vector of its symbols. An ordering is set on
the lexicon so that each depth level corresponds to a token.
    The naive search algorithm for finding proportions, given a user request ru ,
works by trying every possible triplet of requests from the base and test them
using the validation procedure. Using the tree-count, only a linear search of
the base is needed. For each request r1 of the base, the count vector of r1 [ ru
is computed, that is the values of |r1 |s + |ru |s for every symbol s. Given this
vector, the tree is searched for pairs (r2 , r3 ) of forms that fit the count equation,
as given previously. The complexity of the search is then O(|B| ⇥ |L|). While
this reduces the computation time, the issue of sensitivity to the noise in the
base or in the input remains.
                                                                                                           91




4.2      Relaxed Tree-Count Search
In order to enable approximations at the step of triplet searching for indirect
resolution, we adapted the tree-count algorithm to be more flexible to noise.
Instead of looking for quadruplet of requests (3 from the base, 1 from the user)
that are analogical proportions, our approach also explores some that are not.
However, one does not want to consider each of the |B|3 quadruplets that can
be formed. We want to keep track of the distance from which a given quadruplet
is to be an analogical proportion. We define the deviation         of a quadruplet
of sequences (X, Y, Z, T ) as follows3 :
                         X
                      =      abs ((|X|s + |T |s ) (|Y |s + |Z|s ))
                                s2L
The exact tree-count search algorithm retains from a step i only the paths that
verify the counts for all symbols before i. With the relaxed algorithm, only
the paths for which the counts are verified with a deviation     are selected for
the next step. Algorithm 1 achieves a generic tree-count search for a given .
It was designed on the basis of the standard tree-count search from Langlais
and Yvon [6]. The tree-count is searched breath-first. Each pair of nodes sat-
isfying the constraints on the count of symbols is added to the list named
frontier. The paths from other pairs are pruned. We keep track of the cur-
rent while descending the tree, thus each step is performed           times. The
macro eqSumChildren(n1 , n2 , , adj) retrieves every pair of children (c1 , c2 ) –
from n1 and one from n2 – for which the di↵erence between the goal count and
the sum of the occurrences of the current symbol i is less than adj.


    Algorithm 1: Relaxed search using a count-tree
                                           1    2
      Input: A pair of forms Pin = (fin      , fin ), a maximum divergence      and a count-tree T using
               the lexicon L
                                               1      2
      Output: The set of pairs Pout = (fout        , fout , ) from T such that
                   = |count(Pin ) count(Pout )| 
 1    counts      encode(s1in , s2in )
 2    f rontier     {(root(T ), root(T ), 0)}
 3    i    1
 4    while i  |L| ^ f rontier 6= {} do
 5         res     {}
 6         ⌫     counts[L[i]]
 7         forall the (n1 , n2 , ) 2 f rontier do
 8              for adj = 0 !           do
 9                   res    res [ eqSumChildren(n1 , n2 , , adj)
10              end
11         end
12         f rontier     res
13         i    i+1
14    end
15    return {(f1 , f2 , ) : f1 2 p1 .f orms, f2 2 p2.f orms, (p1 , p2 , ) 2 f rontier}




  The proposed relaxation of the algorithm has the e↵ect of retaining up to
2 +1 times more open paths at each step. The coefficient 2 comes from that the
3
     abs() denotes the absolute value for distinction from the count of symbols.
                                                                                             92




deviation can be about adding or removing a symbol. The worst case complexity
however remains in O(n3 ) with n the size of the base, since no more than every
triplet can be explored. This is of course limited by the actual number of paths
in the tree, that is, the set of count-compatible requests pairs (n2 ). This set is
expected to be much smaller than the n2 for a given input request pair, especially
for long sentences. However, it also depends on      and on the dispersion of the
examples in the base.
    The relaxed tree-count search helps decreasing noise sensitivity of formal
analogy on the source, i.e. on requests. However, it has no e↵ect on the noise in
the target domain, i.e. commands. The following section tackles this issue with
a relaxation of the analogical resolution algorithm.


5     Approximate Resolution
5.1   Analogical Dissimilarity
The notion of analogical dissimilarity (AD) introduced by Miclet et al. [11] in-
tends to represent how far a quadruplet of objects is to be a valid analogical
proportion. Hence, an AD of 0 signifies that the quadruplet is a valid proportion.
Analogical dissimilarity is defined for quadruplets of sequences as the alignment
of the symbols of minimal cost. The cost of an alignment itself is defined as the
sum of the AD of each quadruplet of symbols. Finally, the AD of a quadruplet of
symbols can be set depending on the symbols themselves. In [11], it is assumed
that a matrix of similarity is given for the whole alphabet. This is not realistic if
the symbols are words. The general AD between symbols can be formally defined
similarly as for binary values: the AD between a quadruplet of symbols is the
minimum number of symbols that have to be substituted in order for the quadru-
plet to stand as a valid analogical proportion. For example AD(a, b, c, b) = 1.
This definition bounds the AD for symbols to values between 0 and 2. Hence,
the AD for sequences is comprised between 0 and 2n, n being the size of the
alignment of minimal cost. The example below shows an alignment (of minimal
cost) of 4 sequences, along with the costs of each symbol quadruplet alignment.
The total cost of the quadruplet of sequences is AD(X, Y, Z, T ) = 4.
                            X remove ✏ the file  ✏    f.zip
                            Y show ✏ the file named foo.txt
                            Z delete ✏ the file  ✏    f.sh
                            T show me the file named bar.txt
                                 1   1 0 0       0      2

     Note that [11] only consider character level segmentation, the example is
segmented at word level in order to represent the use of AD in our context.
     The authors then propose an algorithm for computing approximate solutions
to analogical equation using AD. The solving process (solvana) is based on
the dynamic programming analogical resolution algorithm [14]. At each step
(i, j, k) of the filling of the three dimensional matrix, every previous cells are
examined, that is all the cells of indices (i di , j dj , k dk ) for all (di , dj , dk ) 2
{0, 1}3 \ (0, 0, 0). The path that corresponds to the alignment of the lowest AD
                                                                                       93




is selected. This is determined by enumerating every character of the alphabet
and computing the AD of the corresponding quadruplet of symbols.
    The complexity of the algorithm is O(m ⇤ n3 ) where m is the size of the
lexicon, and n is the maximum length of the sequences. In our context, the
lexicon is a lot bigger than the set of all the characters used by Miclet. Moreover,
unlike the set of the characters, a lexicon of words can never be exhaustive, and
is always subject to updates. Hence we cannot use the algorithm as is.

5.2   Analogical Dissimilarity on Arbitrary Sized Lexicons
As for the solvana algorithm [11], our proposition is based on the dynamic
programming solving algorithm. However, less transitions are considered for each
cell. In the cell (i, j, k), the possible transitions are from the cells:
                                     X     Y    Z
                             t1 : ( i 1 , j 1 , k )
                             t2 : ( i 1 , j , k 1 )
                             t3 : ( i , j 1 , k )
                             t4 : ( i , j , k 1 )
                             t5 : ( i 1 , j , k )
    This choice was guided by the fact that every other transition can be reduced
to a combination of these ones. Among them, the legal transitions are:
 1. read identical symbols on the X and Y sequences, write nothing on T
 2. read identical symbols on the X and Z
 3. read a symbol from Y and write it to T
 4. read a symbol from Z and write it to T
   They induce no deviation, as they are legitimate for a valid analogy. Below
are the five selected operations that are not legitimate.
 1. read di↵erent symbols on X and Y , no output (virtual substitution)
 2. similarly, read di↵erent symbols on X and Z
 3. read a symbol from Y , write nothing on output (virtual deletion)
 4. similarly, for Z
 5. similarly, for X
    Each illegitimate transition can be used at a cost of 1. As in 4.2, we name
this cost deviation – distinguishing from dissimilarity. Consequently, the four
transitions listed previously have a deviation of 0.
    Substitution and deletion are considered but inserting new symbols implies
to get them from a source. However, enumerating every possible word to insert
from the lexicon is too costly. Also, identifying relevant insertions would require
a non trivial strategy for guiding the search. Hence, we did not consider the
insertion of new symbols.
    As for the algorithm of relaxed search, the relaxed resolution takes the devi-
ation threshold as parameter. During the filling of the three dimensional matrix,
deviations are considered up to the specified threshold. This makes the complex-
ity of the algorithm in O(n3 ), that is equivalent to the initial algorithm.
                                                                                           94




6     Experiments and Results

6.1     Experimental Setup


Our setup is based on the setting and corpus used in [10]. It is composed of 421
associations between requests in French and commands in bash. We used the
dynamic programming algorithm from [14] for the resolution.
    The system takes a natural language request as input and the output is a
command. The direct and indirect resolution strategies are performed indepen-
dently. The direct resolution module searches the base for mixed triplets and
then solves them with the minimum possible deviation  r . The indirect
resolution module searches the example base for all the quadruplets of requests
of the minimum possible deviation  s using the tree-count index. The com-
mands associated with the triplets found are then passed to the resolution step
which attempts to solve the resulting equation with the minimum  r .
    We used two data sets for our experiments4 . The first one, called sp (Same
Person), is composed of associations collected with the same person who wrote
the examples of the base, and the commands still used the same set of parame-
ters. The second one, called np (New Person), contains associations written by
another person while systematically changing the parameters of each command.
Both test sets contain 77 requests and their associated commands for evaluation.



6.2     Results


The tests were conducted by varying the allowed deviation using both sets to
assess the score. Table 1a gives the scores and execution time for the sp and np
test sets. The lines correspond in that order to the number of answers given,
the number of correct answers, the associated values of precision and recall, the
average time per request for an exhaustive search, and the average time per
request when ending the search immediately after the first result found. For
the sp set, the number of answers is consistently increasing with the allowed
deviation, up to 64 of 77. Similarly on the np set, though with a lower increase
(35 of 77). There are less new correct answers on np than on sp. Besides, the
execution time grows a lot as soon as s > 2, especially with the sp set.
    The tests with approximate resolution only are far less time consuming (cf.
table 1b). However, despite an important increase in recall, the precision drops
more than with the relaxed search only. The number of correct answers hardly
increases by few units compared to the default run ( r = 0) and stagnates for
  r    2. These results were partly expected, but show interesting specificities,
which are discussed in the next section.

4
    The datasets can be found at http://perso.limsi.fr/letard/ilar/iccbr analogy2016.zip
                                                                                          95




                                  Table 1: Test results

      (a) Increasing the search deviation        (b) Increasing the solving deviation
              Evaluating on sp                           Evaluating on sp
      s          0    1    2    3    4    5      r           0    1    2    3    4    5
    answers     36 43 50 53 59           64    answers      36 48 55 61 66 71
    correct     35 42 49 51 57           61    correct      35 41 42 42 42 42
    precision 0.97 0.98 0.98 0.96 0.97 0.95    precision 0.97 0.85 0.76 0.69 0.63 0.59
    recall    0.47 0.56 0.65 0.69 0.77 0.83    recall     0.47 0.62 0.71 0.79 0.85 0.92
    time/req* 0.4 2.4 14.1 35.5 82.1 163.8     time/req* 0.4 0.9 1.3 1.8 2.2 2.7
    time/req 0.3 1.3 5.0 13.7 32.9 67.0        time/req 0.3 0.4 0.5 0.5 0.6 0.6
              Evaluating on np                           Evaluating on np
      s          0    1    2    3    4    5      r           0    1    2    3    4    5
    answers      9 10 14 18 27           35    answers       9 20 30 39 44 52
    correct      9 10 10 11 11           11    correct       9 10 12 12 12 12
    precision    1    1 0.71 0.61 0.41 0.31    precision     1 0.50 0.40 0.31 0.27 0.23
    recall    0.12 0.13 0.18 0.23 0.35 0.45    recall     0.12 0.26 0.39 0.51 0.57 0.68
    time/req* 0.0 0.5 3.1 10.5 27.0 56.4       time/req* 0.4 0.9 1.3 1.8 2.2 2.7
    time/req 0.0 0.3 2.2 8.1 20.2 42.1         time/req 0.3 0.4 0.5 0.5 0.6 0.6



7         Contrastive Discussion

7.1       Findings


The relaxation of the counting constraint for searching requests in the example
base allowed a remarkable increase of the recall of the system, with a minimal
impact on its precision on the sp set. The most limiting factor for an application
is actually the execution time which rapidly grows out of control. Also, the time
complexity has to be watched carefully while increasing the size of the example
base. Efficient selection strategies may be necessary in order to continue using
the counting relaxation within reasonable delays. The progress are far lower
while testing on the np test set. Indeed, as was highlighted in [10], successful
analogical resolution on this particular test set mostly involves direct analogies.
The counting relaxation only a↵ects the indirect resolution, as counting is only
used at the quadruplet searching phase.
    To summarize, while the relaxation allows relevant approximations in the
source language quadruplet, the target language triplet still has to have an exact
analogical solution in order to produce the answer. This also applies to mixed
triplets for direct resolution. Although we must be cautious while making strong
conclusions due to the small size of our example base, it can be conclusively said
that FAR has an important progression margin towards noise handling. As for
the results on our corpora, applying a search deviation of 2 words seems to be a
good compromise between computing time, precision and recall for a practical
application.
                                                                                       96




7.2   Related Work

Our modification of the dynamic programming analogical resolution algorithm,
serves a di↵erent purpose than the one proposed by [11]. Their use is focused
on the production of outputs containing deviations with the concern of giving
an answer as often as possible when the deviation is not too high. However,
enumerating the set of all the tokens in order to consider every possible insertion,
even while eliminating most of them, cannot be done while segmenting at word
level. The value of analogical dissimilarity is defined between characters by a
predefined set of features on the alphabet. This is an interesting point to explore
in our case, in order to weight more accurately the approximate substitutions of
words. It may also be automatically determined using some similarity on words.



8     Conclusion and Future Work

We presented two propositions of relaxation on two algorithms used for language
transfer by analogy. Our hypothesis was that these relaxations could improve the
recall with a limited impact on the precision.While the approximate analogical
resolution did not yield very high scores, the relaxed tree-count search, despite
a high computational cost, showed a promising increase of the correct answers.
    Since our application falls whithin human-computer interaction, one way the
system may be improved is by asking a confirmation to the user before choosing
the answer. Indeed, after performing a relaxed tree-count search, the validation
step is not relevant, as the deviation is higher than 0. However, three of the
four sentences can be set as an analogical equation and solved. This gives an
alternative version of the fourth sentence. This version cannot be used to create
an answer because it is absent from the example base, however it can be useful in
interactive context. If no result is found with 0 deviation, the confidence in the
output is supposed to decrease. Also, possibly many solutions with deviation can
be returned, not all of them being correct. In this case, the system can use the
generated request in order to ask the user for a pre-confirmation. If positive, it
will higher the confidence in the corresponding solution. If negative, the system
continues with the next solution.
    This work suggests other interesting perspectives on several aspects of the
approaches. An important track is open towards reducing the computation time
of the relaxed tree-count search. As we showed, greater values of deviation keep
producing new correct answers with a limited noise in output, but the delay
becomes unrealistic. One may attempt to reduce it with a more informed defini-
tion of deviation that depends on the content of the tokens, or possibly on some
external knowledge. Another track is to change the token unit to a sequence of
words where this is possible, this would enable the easier processing of deviation
between multiword expressions. Types of deviations may also be considered in
order to avoid the deletion or replacement of crucial tokens such as parameters.
                                                                                            97




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